Methods of fabrication for flip-chip image sensor packages

ABSTRACT

Methods for packaging optically interactive devices such as images sensors. In a first embodiment of the invention, conductive traces are formed directly on the second surface of a transparent substrate and an image sensor chip is bonded to the traces. Discrete conductive elements are attached to the traces and extend below a back surface of the image sensor chip. In a second embodiment, a secondary substrate having conductive traces formed thereon is secured to transparent substrate. In a third embodiment, a backing cap having a full array of attachment pads is attached to the transparent substrate of the first embodiment or the secondary substrate of the second embodiment. In a fourth embodiment, the secondary substrate is a flex circuit having a mounting portion secured to the second surface of the transparent substrate, and a backing portion bent over adjacent to the back surface of the image sensor chip.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of application Ser. No.10/230,654, filed Aug. 29, 2002, pending.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to packaging for opticallyinteractive electronic devices. More particularly, the present inventionrelates to a package for a solid-state image sensor particularlysuitable for high input/output (I/O) count devices wherein an imagesensor chip is mounted in flip-chip fashion to a transparent substrateor to a secondary substrate secured to the transparent substrate.

[0004] 2. State of the Art

[0005] Optically interactive electronic devices, for example, chargecoupled device (CCD) image sensors or complementary metal-oxidesemiconductor (CMOS) image sensors, are typically packaged within ahousing for subsequent connection to higher-level packaging such as alarger circuit assembly in the form of a carrier substrate. The housingprovides electrical interconnection to the larger circuit assembly,provides protection from the surrounding environment and allows light orother forms of radiation to pass through to sensing circuitry located onthe image sensor device. In the prior art, package formation has oftenbeen accomplished by placing an image sensor device in the form of asemiconductor chip into the cavity of a plastic or ceramic housing, wirebonding electrical connection points on the semiconductor chip toconductive pads associated with the housing and sealing a window ortransparent cover over the cavity. The materials and structure involvedwith this packaging technique require a fabrication process that can betime consuming and requires several precision assembly steps. Wirebonding, for instance, involves special considerations during packageformation due to the fragile nature of bond wires and their associatedconnection points, and also may call for excessive package depth orthickness in order to accommodate the arched wire bond loops within thepackage cavity. Further, each assembly step increases the opportunityfor contamination or damage to the image sensor device itself, raisingdefect levels and slowing production time to avoid such damage andcontamination. Due to the extremely cost-competitive nature of today'ssemiconductor industry, even small improvements in product yield andproduction time are of value, especially when considered in terms of thehigh volume of components being manufactured.

[0006] In response to the above-noted shortcomings of the existingpackaging techniques, various structures using flip-chip mounting of animage sensor chip have been developed in an attempt to simplify theconstruction of image sensor packages. U.S. Pat. No. 6,144,507 toHashimoto and U.S. Pat. No. 5,867,368 to Glenn, for example, eachdisclose an image sensor chip mounted directly to a printed circuitboard (PCB). An image sensor chip is mounted in flip-chip fashion overan aperture within the PCB, and a transparent cover is either attacheddirectly to the active surface of the chip or bonded to the side of thePCB opposite that to which the image sensor chip is attached and overthe aperture. Although these methods eliminate the difficultiesassociated with wire bonding and forming a housing for the image sensorchip, the illustrated PCB's are very large with respect to the size ofthe image sensor chip and the transparent cover. It is unclear from theaforementioned patents whether the PCB's comprise discrete image sensorpackages suitable for attachment to a larger circuit assembly, orthemselves comprise large circuit assemblies simply having an imagesensor chip mounted directly thereto, without the benefit of a packageor housing.

[0007] Another packaging approach has been to use the transparent coveritself as a foundation for an image sensor package. U.S. Pat. No.5,786,589 to Segawa et al. uses this approach by adhesively bonding aTAB sheet to a glass substrate and bonding an image sensor chip to theTAB tape with an anisotropically conductive film. This design requires aspecialized substrate attachment technique due to the TAB-typeconnection leads. Moreover, the conductive film risks interference withsensing circuitry on the image sensor chip and requires the formation ofdummy leads or dam structures to compensate for this problem. U.S. Pat.No. 6,342,406 to Glenn et al. and U.S. Pat. No. 5,352,852 to Chun eachbond an image sensor chip to a transparent substrate by formingconductive traces directly on the substrate. Glenn et al., however, usesa ball mounting arrangement on the first surface of the transparentsubstrate that requires the formation of vias through the substrate toconnect interior and exterior traces formed thereon. The arrangementalso requires an aperture be formed within any substrate carrying thepackage to provide optical access to the active surface of the imagesensor chip, as the image sensor active surface faces the attachmentside of the package. Chun uses a lead arrangement that requires thepackage to be mounted within a substrate mounting depression or theaddition of outleads which may be susceptible to damage during packagehandling and may not be suitable for high I/O sensor devices. Chunfurther requires the use of a frame of insulating tape to space theimage sensor chip from the interior of the transparent substrate.

[0008] As is evident from the foregoing review of the current state ofthe art in image sensor packaging, a need exists for an improved imagesensor packaging structure that is simple to fabricate, suitable for usewith high I/O sensor devices, durable and easily mounted to a largercircuit assembly without the use of special substrate apertures ordepressions.

BRIEF SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, image sensor packaginghaving the above-described and other beneficial characteristics andmethods for fabrication thereof are provided. An image sensor chip isflip-chip mounted to conductive traces on a first surface of atransparent substrate. The active surface of the image sensor chip isprotected from contamination after mounting by depositing a bead ofsealant around the periphery of the image sensor chip between the activesurface of the image sensor chip and the first surface of the substrate,thus eliminating any need for additional damming structures or spacingframes as used in the prior art. Discrete conductive elements suchsolder balls or columns are attached to ends of the conductive traceswhich form an array pattern, the discrete conductive elements extendingtransversely from the conductive traces on the first surface to asubstantially common plane at a level beyond a back surface of the imagesensor chip. The resulting structure comprises a board-over-chip (BOC)package arrangement that provides high I/O connectivity for the imagesensor chip and is easily mounted to a carrier substrate such as aprinted circuit board (PCB) without requiring the formation of specialapertures therein.

[0010] In a first exemplary embodiment of the present invention,conductive traces are formed directly on the first surface of thetransparent substrate and an image sensor chip is flip-chip mounted tofirst attachment points of the conductive traces. The conductive tracesextend beyond the periphery of the image sensor chip, and discreteconductive elements are joined to or formed on second attachment pointsof the conductive traces in an array pattern around the image sensorchip.

[0011] In a second exemplary embodiment of the present invention, asecondary substrate having the conductive traces formed thereon issecured to the first surface of the transparent substrate. An imagesensor chip is flip-chip mounted to first attachment points of theconductive traces. The conductive traces extend beyond the periphery ofthe image sensor chip and discrete conductive elements are formed in anarray pattern as in the first exemplary embodiment.

[0012] In a third exemplary embodiment of the present invention, abacking cap is placed over the back surface of the image sensor chip.The side of the backing cap facing toward the image sensor chip carriescontacts placed in electrical communication with the conductive tracesformed on the transparent substrate or the secondary substrate whichare, in turn, in electrical communication with the image sensor chip.Because the backing cap covers the back surface of the image sensorchip, discrete conductive elements for connection to external circuitrymay be formed in a full array pattern including the area underneath theimage sensor chip.

[0013] In a fourth exemplary embodiment of the present invention, thesecondary substrate secured to the transparent substrate is in the formof a flex circuit having the conductive traces formed thereon. The flexcircuit includes a backing portion that is folded over the back surfaceof the image sensor chip. The backing portion has discrete conductiveelements formed in a full array pattern as in the third exemplaryembodiment.

[0014] In a further variation to any of the above-described packageembodiments, an array of image sensor packages may be simultaneouslyformed on one large transparent substrate, which is then cut orotherwise divided or singulated to form multiple individual image sensorpackages.

[0015] Other and further features and advantages of the presentinvention will be apparent from the following descriptions of thevarious exemplary embodiments read in conjunction with the accompanyingdrawings. It will be understood by one of ordinary skill in the art thatthe following are provided for illustrative and exemplary purposes only,and that numerous combinations of the elements of the variousembodiments of the present invention are contemplated as within thescope of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016] In the drawings, which illustrate what is currently considered tobe the best mode for carrying out the invention:

[0017]FIG. 1 is a perspective view showing an image sensor chipcontained within image sensor packaging according to the presentinvention.

[0018]FIG. 2 is a side view showing a transparent substrate according tothe present invention.

[0019]FIG. 3 is a sectional side view showing an image sensor packageaccording to a first embodiment of the present invention.

[0020]FIG. 4 is an underside view showing a second surface of atransparent substrate for the image sensor package depicted in FIG. 3.

[0021]FIG. 5 is a side view showing the image sensor package depicted inFIG. 3 mounted to a carrier substrate.

[0022]FIG. 6 is a flow chart showing a method of fabrication accordingto the first embodiment of the present invention.

[0023]FIG. 7 is a sectional side view showing an image sensor packageaccording to a second embodiment of the present invention.

[0024]FIG. 8 is a plan, underside view showing a secondary substrate forthe image sensor package depicted in FIG. 7.

[0025]FIG. 9 is a flow chart showing a method of fabrication accordingto the second embodiment of the present invention.

[0026]FIG. 10 is a sectional side view showing a backing cap for animage sensor package according to a third embodiment of the presentinvention.

[0027]FIG. 11 is a top plan view of the backing cap depicted in FIG. 10.

[0028]FIG. 12 is a sectional side view showing an image sensor packageaccording to the third embodiment of the present invention.

[0029]FIG. 13 is a flow chart showing a method of fabrication accordingto the third embodiment of the present invention.

[0030]FIGS. 14A and 14B are perspective views showing a flex circuitaccording to a fourth embodiment of the present invention.

[0031]FIGS. 15A and 15B are sectional side views showing an image sensorpackage according to the fourth embodiment of the present invention.

[0032]FIG. 16 is a flow chart showing a method of fabrication accordingto the fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Referring in general to the accompanying drawings, variousaspects of the present invention are illustrated to show the structureand methods for assembly of an image sensor package formed on atransparent substrate. Common elements and features of the illustratedembodiments are designated by the same or similar reference numerals. Itshould be understood that the figures presented are not meant to beillustrative of actual views of any particular portion of the actualdevice structure, but are merely idealized schematic representationswhich are employed to more clearly and fully depict the invention. Itshould further be understood that, while depicted in terms of an imagesensor, the package embodiments and methods presented herein would workwell for other types of optically interactive electronic devices. Theterm “optically interactive” as used herein encompasses devicessensitive to various wavelengths of light or other forms of radiation,such as, but not limited to, CCD and CMOS image sensors, EPROM's, andphotodiodes, as well as light-emitting devices such as semiconductorlasers and light-emitting diodes.

[0034]FIG. 1 shows a perspective view of an exemplary image sensor chip2 suitable for use with the various embodiments of the presentinvention. Image sensor chip 2 includes an active surface 4 and a backsurface 6. Active surface 4 and back surface 6 are bounded by sides 8,also termed the “periphery” of image sensor chip 2. Active surface 4includes sensing circuitry 10 in a central portion and bond pads 12formed outwardly of sensing circuitry 10 and around the perimeter ofactive surface 4. As used herein, the term “bond pads” includes not onlybond pads directly connected to underlying sensing circuitry 10 but alsobond pad locations removed from original locations using aredistribution layer extending over active surface 4 as known in theart. Bond pads 12 are depicted in a single row along each of the foursides 8 of image sensor chip 2, but other arrangements are possible, forexample and not by way of limitation, having bond pads 12 formed alongfewer sides or in multiple rows along one or more sides. If multiplerows are used, the bond pads 12 of one row may be staggered or offsetfrom those of an adjacent row. Conductive bumps 14 (only some shown byway of example) are formed on bond pads 12 to enable flip-chipattachment of image sensor chip 2 and will be described in furtherdetail below. For certain types of image sensors, micro-lenses 16 may beformed over sensing circuitry 10 to aid in the reception of light.

[0035]FIG. 2 shows a side view of an exemplary transparent substrate 18serving as the primary package structure for the various embodiments ofthe present invention. Transparent substrate 18 includes a first surface20 and a second surface 22. Transparent substrate 18 may be formed ofglass, plastic or any other substrate material that is suitablytransmissive of light or other forms of radiation. Accordingly, the term“transparent” is not used in its literal sense, but is descriptive of asubstrate material exhibiting sufficient transmissivity of light atselected wavelengths sufficient for operation of image sensor chip 2. Aplate of borosilicate glass is one specific, and currently preferred,example of a suitable material for transparent substrate 18. Transparentsubstrate 18 may also provide an auxiliary optical function, forinstance, by forming first surface 20 into a lens, grating or othersuitable configuration to provide light focusing, refraction ordispersion capabilities or by using a material for or coating oftransparent substrate 18 that prevents selected wavelengths of lightfrom passing therethrough to sensing circuitry 10.

[0036] Turning to FIGS. 3 through 6, a first embodiment according to thepresent invention is illustrated. FIG. 3 shows a sectional side view ofan image sensor package 24 wherein conductive traces 26 (thicknessenlarged for clarity) are formed directly on second surface 22 oftransparent substrate 18. As seen in FIG. 4, which is an underside planview of second surface 22 as oriented in FIG. 3, conductive traces 26have first attachment points 28 formed at locations around the center oftransparent substrate 18 and corresponding to the spacing of bond pads12 on image sensor chip 2. Spreading out from the center of transparentsubstrate 18, conductive traces 26 have second attachment points 30formed in an array pattern. For purposes of illustration, secondattachment points 30 have been depicted in a single row running aroundthe center and proximate the periphery of transparent substrate 18. Itshould be understood, however, that the number of rows employed may bebased on factors such as the number and arrangement of bond pads 12 onimage sensor chip 2, and may comprise several rows of second attachmentpoints 30. Conductive traces 26 may be formed on second surface 22 oftransparent substrate 18 using a variety of techniques. For instance, aconductive or conductor-filled liquid epoxy or resin could be printed,screen-printed or otherwise dispensed onto second surface 22 in thedesired pattern and then cured to form conductive traces 26.Alternatively, a layer of conductive material such as metal or dopedsilicon may be formed over the entirety of second surface 22, and thenselectively etched to form conductive traces 26. As yet anotherapproach, adhesively coated preformed traces carried by a removablebacking layer may be applied to transparent substrate 18 and then thebacking layer removed.

[0037] Returning to FIG. 3, an image sensor chip 2 is flip-chip mountedto first attachment points 28 by bonding with conductive bumps 14 suchthat sensing circuitry 10 on active surface 4 is exposed through thecentral portion of transparent substrate 18. The term “bumps” includes,without limitation, conductive structures configured as balls, bumps,columns, pillars and studs. In the various embodiments of the presentinvention, conductive bumps 14 are formed of materials known in the artfor use in flip-chip bonding. Suitable materials may include, but arenot limited to, conductive or conductor-filled epoxy, eutectic tin/leadsolder and gold. Conductive bumps 14 may be formed of one material, notnecessarily conductive, and coated with another. Alternatively, a stripor segment of an anisotropically conductive adhesive film may beemployed in lieu of a plurality of conductive bumps 14. In the casewhere sensing circuitry 10 is covered by micro-lenses 16, conductivebumps 14 are formed to a sufficient thickness so as to leave a verticalgap 32 between micro-lenses 16 and second surface 22 to enablemicro-lenses 16 to properly receive light through transparent substrate18.

[0038]FIG. 3 further shows discrete conductive elements 34 attached tosecond attachment points 30 and extending downwardly from transparentsubstrate 18 to a plane at a level below back surface 6 of image sensorchip 2. By extending beyond the back surface 6 of image sensor chip 2,discrete conductive elements 34 enable image sensor package 24 to bemounted to a carrier substrate 38 (FIG. 5) without the need for adepression or cavity within the surface of carrier substrate 38 toaccommodate image sensor chip 2. Moreover, since discrete conductiveelements 34 interface with carrier substrate 38 below or “behind” imagesensor package 24, active surface 4 of image sensor chip 2 facesoutwardly. Therefore, an aperture is not required within carriersubstrate 38 to expose active surface 4. In a presently preferredembodiment, discrete conductive elements 34 are structures that extenddownwardly in a direction perpendicular to the plane of second surface22, such as solder balls or columns. These structures are lesssusceptible to damage during handling than the lead arrangements used inprior art packaging. They may also be formed in multiple rows, makingthem more suitable for packaging of high I/O devices. The solder ballsor columns may be formed entirely of a eutectic tin/lead solder, or mayhave a solid metal core surrounded by solder. Forming discreteconductive elements of other materials such as conductive orconductor-filled epoxy or anisotropically conductive materials is alsowithin the scope of the present invention, as long as they can be sizedand configured to meet the desired height and pitch requirements.

[0039] A bead of sealant 36 is deposited around the sides 8 or peripheryof image sensor chip 2 and contacts second surface 22 of transparentsubstrate 18. Sealant 36 protects active surface 4 of image sensor chip2 from outside environmental damage and further mechanically secures theintegrity of the flip-chip bonds extending between bond pads 12 of imagesensor chip 2 and conductive traces 26 of transparent substrate 18.Because sealant 36 is placed around the periphery of active surface 4after attachment of image sensor chip 2, there is no need for additionaldamming structures or spacing frames which complicate the fabricationprocess. Nonexhaustive examples of suitable sealant 36 material includea viscous liquid or gelled epoxy or silicone deposited around imagesensor chip 2 and cured in place.

[0040]FIG. 5 shows a side view of image sensor package 24 mounted tocarrier substrate 38, wherein discrete conductive elements 34 are formedas solder balls which have been reflowed to bond to conductive terminalpads 40 on the surface of carrier substrate 38.

[0041]FIG. 6 shows a flow chart of an exemplary method of fabricationfor the first embodiment of the present invention. First, in action 100,conductive traces 26 are formed on second surface 22 of transparentsubstrate 18. In action 102, image sensor chip 2 is flip-chip mounted bybonding conductive bumps 14 to first attachment points 28. Next, inaction 104, a bead of sealant is deposited around image sensor chip 2,contacting sides 8 and transparent substrate 18. Finally, in action 106,discrete conductive elements 34 are formed on or attached to secondattachment points 30, and image sensor package 24 is completed.

[0042] A second embodiment according to the present invention isillustrated in FIGS. 7 through 9. FIG. 7 shows a sectional side view ofan image sensor package 42. A secondary substrate 44 having aperture 46and conductive traces 26 (enlarged for clarity) formed thereon issecured to second surface 22 of the transparent substrate 18, and imagesensor chip 2 is flip-chip mounted to secondary substrate 44. Secondarysubstrate 44 may be, for example, a PCB formed of an FR-4 or FR-5laminate, a BT epoxy resin, a ceramic, or silicon with conductive traces26 formed thereon by conventional PCB fabrication techniques, such asthe aforementioned printing, etching, etc. The secondary substrate 44 isthen secured to transparent substrate 18 such as with an adhesivematerial applied to the PCB and/or transparent substrate 18.Alternatively, secondary substrate 44 may be formed of a polymer filmsuch as a polyimide having conductive traces formed on one side and anadhesive coating on the opposite side for securing to transparentsubstrate 18. A pressure-sensitive, heat or light-curable adhesive maybe employed. Nonadhesive bonding, such as heat bonding, of secondarysubstrate 44 to transparent substrate 18 may be employed with suitablematerials.

[0043] As seen in FIG. 8, which is a plan underside view of secondarysubstrate 44, conductive traces 26 have first attachment points 28 andsecond attachment points 30, and spread out from aperture 46 in apattern similar to that of the first embodiment. While depicted as beingon an outside surface of secondary substrate 44 facing image sensor chip2, conductive traces 26 may reside within secondary substrate 44 or belocated on the opposite side thereof and include interlevel connections(vias) respectively extending to the first and second attachment points28 and 30. Conductive bumps 14 on image sensor chip 2 are bonded tofirst attachment points 28 such that sensing circuitry 10 is exposedthrough aperture 46. Discrete conductive elements 34 having the samestructure as in the first embodiment are attached to second attachmentpoints 30. A bead of sealant 36 is also deposited around the sides 8 ofimage sensor chip 2, but sealant 36 contacts secondary substrate 44rather than transparent substrate 18 as in the first embodiment.

[0044]FIG. 9 shows a flow chart of an exemplary method of fabricationfor the second embodiment of the present invention. First, in action200, secondary substrate 44 having aperture 46 and conductive traces 26is adhesively secured to transparent substrate 18. In action 202, imagesensor chip 2 is flip-chip mounted by bonding conductive bumps 14 tofirst attachment points 28. Next, in action 204, a bead of sealant isdeposited around image sensor chip 2, contacting sides 8 and secondarysubstrate 44. Finally, in action 206, discrete conductive elements 34are formed on or attached to second attachment points 30, and imagesensor package 42 is completed.

[0045] For image sensor devices with higher I/O requirements, a fullarray pattern of discrete conductive elements may be desirable forattaching an image sensor package to a carrier substrate. Turning toFIGS. 10 through 13, a third embodiment of the present inventionproviding a full array pattern is illustrated. FIG. 10 shows a sectionalside view of a backing cap 48 that is constructed to extend over backsurface 6 and sides 8 of image sensor chip 2. Backing cap 48 includesbase 50 and sidewalls 52 around and extending transversely from theperimeter of base 50. Base 50 and sidewalls 52 may be formed, forexample, of conventional PCB materials such as glass-reinforced fiber,polymeric or ceramic materials. Conductive lines 54 extend throughbacking cap 48 from attachment points 56 exposed on sidewalls 52 toattachment pads 58 exposed on base 50. Because attachment pads 58 areformed on base 50, they may be arranged in a fully populated arrayacross the entire area or “footprint” of the image sensor package,providing more I/O interfaces for a sensor device contained therein.

[0046] Backing cap 48 may be used in combination with elements of bothimage sensor package 24 of the first embodiment and image sensor package42 of the second embodiment. Rather than attaching discrete conductiveelements 34 to second attachment points 30, backing cap attachmentpoints 56 may be bonded to second attachment points 30 of conductivetraces 26 for electrical communication with attachment pads 58. Secondattachment points 30 and backing cap attachment points 56 may be bondedin a variety of ways, such as by application of conductive orconductor-filled epoxy or by forming a solder joint between the two. Aframe comprising a film of anisotropically conductive adhesive materialmay also be applied between sidewalls 52 and transparent substrate 18 orsecondary substrate 44, depending on the image sensor package embodimentelements used with backing cap 48. This approach electrically connectsand bonds second attachment points 30 and backing cap attachment points56, and further acts to seal backing cap 48 into place. With the thirdembodiment, second attachment points 30 may be formed much smaller thanin the first two embodiments, as they are not required to support theformation of discrete conductive elements 34. Accordingly, an increasednumber of second attachment points 30 may be patterned around theoutside of image sensor chip 2 for bonding with a corresponding numberof backing cap attachment points 56. This makes it possible toelectrically communicate with a fully populated array of attachment pads58 for higher I/O connectivity. FIG. 11 shows a top plan view of backingcap 48 with an exemplary single row pattern of backing cap attachmentpoints 56. It should also be noted that conductive lines 54 may beformed to extend from backing cap attachment points 56 and around theexterior of sidewalls 52 and over the back surface of base 50 toattachment points 58. Similarly, for simplicity, the portions ofconductive lines 54 extending through sidewalls 52 may comprise viasleading to a redistribution layer of conductive traces formed over theback surface of base 50.

[0047]FIG. 12 shows a sectional side view of an image sensor package 60according to the third embodiment of the present invention using atransparent substrate 18 with conductive traces 26 formed directly onsecond surface 22, as in the first embodiment. After electricalconnection is made between backing cap attachment points 56 andattachment points 30 of conductive traces 26, backing cap 48 is sealedto transparent substrate 18 with a layer or bead of dielectric adhesive62. Alternatively, and as previously noted, an anisotropicallyconductive adhesive may be used to both electrically bond secondattachment points 30 and backing cap attachment points 56 and sealbetween backing cap 48 and transparent substrate 18. Discrete conductiveelements 34 are attached to or formed on attachment pads 58. Discreteconductive elements 34 may be formed as structures and of materialssimilar to those described in conjunction with the first and secondembodiments of the present invention, but will not require as large aheight as they are already located at a point below image sensor chip 2.Alternatively, since attachment pads 58 reside on a plane on the secondsurface of image sensor package 60, discrete conductive elements 34 maybe omitted and attachment pads 58 directly attached to conductiveterminal pads 40 on carrier substrate 38 in a land-grid array-typearrangement.

[0048]FIG. 13 shows a flow chart of an exemplary method of fabricationfor the third embodiment of the present invention. First, in action 300,conductive traces 26 are formed on second surface 22 of transparentsubstrate 18 when using the packaging structure of the first embodiment.Alternatively, in action 300′, secondary substrate 44 having aperture 46and conductive traces 26 is adhesively secured to transparent substrate18 when using the packaging structure of the second embodiment. Inaction 302, image sensor chip 2 is flip-chip mounted by bondingconductive bumps 14 to first attachment points 28. In action 304, a beadof sealant is deposited around image sensor chip 2, contacting sides 8and transparent substrate 18 or secondary substrate 44 depending on thepackage structure used. Because image sensor chip 2 will be covered andsealed by backing cap 48, the sealant of action 304 may optionally be,and preferably is, omitted. Next, in action 306, backing cap 48 issecured in place and second attachment points 30 and backing capattachment points 56 are bonded for electrical communication. Finally,in action 308, if a land-grid-array type package is not desired,discrete conductive elements 34 are formed on or attached to the fullarray of attachment pads 58.

[0049] A fourth embodiment of the present invention that is also capableof providing a full array of I/O interfaces is illustrated in FIGS. 14Athrough 16. The fourth embodiment of the present invention is avariation of the second embodiment, wherein secondary substrate 44 is inthe form of a flex circuit 64 having conductive traces 26 formedthereon. Flex circuit 64 is constructed of conventional flexible circuitmaterials such as a flexible polyimide film having conductive traces 26formed on or within the film. As used herein, the term “flexible” meansany substrate material that may be substantially bent over itself orfolded without causing substantial damage to the flex circuit andspecifically the conductive traces 26 thereof. FIGS. 14A and 14B showexemplary second and first surface perspective views of flex circuit 64.Flex circuit 64 includes a mounting portion 66 and a backing portion 68.Mounting portion 66 includes aperture 46 as in the second embodiment.First attachment points 28 of conductive traces 26 are patterned aroundaperture 46 on a first side 70 of flex circuit 64. However, rather thanforming second attachment points 30 in a pattern around aperture 46,conductive traces 26 (only some shown for clarity) extend onto backingportion 68 through vias (see vias 27 in broken lines in FIGS. 15A and15B) and second attachment points 30 are formed in a fully populatedarray pattern on a second side 72 of flex circuit 64. It should beunderstood that conductive traces 26, while being depicted as straightlines in FIG. 14A for the purposes of illustration, would be routed suchthat each conductive trace 26 would terminate at a separate secondattachment point 30 on second side 72. Vias 27 may be etched into flexcircuit 64, filled by electroless or electroplating, or filled with aconductive or conductor-filled polymer, after which second attachmentpoints 30 are formed thereover as by, for example, formation orapplication of a conductive layer, patterning and etching.

[0050]FIG. 15A shows a sectional side view of an image sensor package 74according the fourth embodiment of the present invention. Mountingportion 66 is adhesively secured to transparent substrate 18 in the samemanner as secondary substrate 44 in the second embodiment. Backingportion 68 extends laterally outwardly from an edge of transparentsubstrate 18. Conductive bumps 14 on image sensor chip 2 are bonded tofirst attachment points 28 such that sensing circuitry 10 is exposedthrough aperture 46. A bead of sealant 36 is also deposited around thesides 8 of image sensor chip 2 and contacts first side 70 of flexcircuit 64.

[0051] As seen in FIG. 15B, backing portion 68 is subsequently bent overor folded such that the full array of second attachment points 30 facesin a downward direction below image sensor chip 2. In a presentlypreferred embodiment, a first side 78 of a rigid substrate 76 isadhesively attached to backing portion 68 on first side 70 of flexcircuit 64 for support when image sensor package 74 is later placed oncarrier substrate 38. Rigid substrate 76 may be prefabricated with flexcircuit 64 before connection of image sensor chip 2 thereto, or may beattached at a later point during formation of image sensor package 74.Rigid substrate 76 may be formed of any suitably rigid material. It maybe formed, for example, of a metal (suitably electrically insulated fromconductive traces 26) which would also aid in heat dissipation whenattached to image sensor chip 2. Furthermore, rigid substrate 76 mayitself be formed with conductive traces with ends extending fromattachment points 30 to locations over vias arranged to correspond withvias 27 and disposed on the outside of backing portion 68 with its viasand aligned with vias 27 on flex circuit 64. A second side 80 of rigidsubstrate 76 is further adhesively attached to back surface 6 of imagesensor chip 2 to hold flex circuit 64 in the folded position.Conventional adhesives may be used for attaching rigid substrate 76 toflex circuit 64 and image sensor chip 2. Alternatively or additionally,rigid substrate 76 may be held in place with stand-off structures 82attached between second side 80 thereof and first side 70 of flexcircuit 64 on mounting portion 66. Stand-off structures 82 may beintegrally formed with rigid substrate 76 (as by molding) and attachedto mounting portion 66, or may be separate structures attached by anyknown methods, for instance, by adhesive bonding or press-fitting intoapertures therein.

[0052] As with backing cap 48 in the third embodiment, discreteconductive elements 34 may be attached to or formed on second attachmentpoints 30, or may be omitted to form a land-grid-array type package.

[0053]FIG. 16 shows a flow chart of an exemplary method of assembly forthe fourth embodiment of the present invention. First, in action 400,mounting portion 66 having aperture 46 and first attachment points 28 isadhesively secured to transparent substrate 18. In action 402, imagesensor chip 2 is flip-chip mounted by bonding conductive bumps 14 tofirst attachment points 28. In action 404, a bead of sealant isdeposited around image sensor chip 2, contacting sides 8 and first side70 of flex circuit 64. In action 406, backing portion 68 havingoptionally preattached rigid substrate 76 and a fully populated array ofsecond attachment points 30 is bent over and secured in place with anadhesive material previously applied to second side 80 of rigidsubstrate 76 and/or to back surface 6 of image sensor chip 2.Alternatively or additionally, backing portion 68 is secured by the useof stand-off structures 82. Finally in action 408, if a land-grid-arraytype package is not desired, discrete conductive elements 34 are formedon or attached to the full array of second attachment points 30 onsecond side 72 of flex circuit 64.

[0054] In a further variation to any of the above-described packageembodiments, an array of image sensor packages may be simultaneouslyformed on one large transparent substrate 18, which is then cut orotherwise divided to form multiple individual image sensor packages. Themethod of assembly for each of the embodiments may proceed in the samefashion as previously described, with singulation occurring, with theexception of the fourth embodiment, after attachment of discreteconductive elements 34 or backing cap 48. Of course, singulation may becarried out at an earlier point in the package fabrication process if sodesired. Further, it is contemplated that backing caps 48 might also beconstructed as a unitary array of backing caps 48 (molded, for example,with runners extending therebetween) which may then be divided alongwith the large transparent substrate 18 during singulation. In addition,if a secondary substrate is employed in accordance with the secondembodiment, it may be of like size and shape to that of the transparentsubstrate, applied thereto and singulated therewith.

[0055] All of the disclosed embodiments of the present invention providedurable image sensor packaging that is simple to fabricate, suitable forhigh I/O sensor devices and easily mounted to a larger circuit assemblywithout the use of special carrier substrate apertures or depressions.Although the present invention has been depicted and described withrespect to the illustrated embodiments, various additions, deletions andmodifications are contemplated within its scope or essentialcharacteristics. For instance, sealant 36 may be deposited to cover theentire sides 8 and back surface 6 of image sensor chip 2 for greaterprotection, or an additional deposition of another encapsulant materialcould be used for this purpose. Also, actions of the exemplary assemblymethods could be carried out in a different order, such as by attachingdiscrete conductive elements 34 to backing cap 48 or flex circuit 64 ina prefabrication process. Furthermore, while described in the context ofan image sensor package, the present invention has utility for thepackaging of numerous types of optically interactive electronic devices.The scope of the present invention is, therefore, indicated by theappended claims rather than the foregoing description. All changes whichcome within the meaning and range of equivalency of the claims are to beembraced within their scope.

What is claimed is:
 1. A method for fabricating an electronic devicepackage comprising: forming a plurality of conductive traces on asurface of a transparent substrate, each conductive trace of theplurality of conductive traces having a first attachment point and asecond attachment point; providing an optically interactive electronicdevice having at least one bond pad on an active surface thereof;bonding the at least one bond pad of the optically interactiveelectronic device to the first attachment point of a conductive trace ofthe plurality of conductive traces; and providing at least one discreteconductive element on the second attachment point of the conductivetrace such that the at least one discrete conductive element extendsoutwardly from the transparent substrate within an outside perimeterthereof from the second attachment point in a direction perpendicular toa plane of the surface of the transparent substrate and to a levelbeyond a back surface of the optically interactive electronic device. 2.The method according to claim 1, wherein forming a plurality ofconductive traces on a second surface of a transparent substratecomprises forming the second attachment points of the plurality ofconductive traces in at least one row extending adjacent a perimeterportion of the surface of the transparent substrate.
 3. The methodaccording to claim 2, further comprising: forming the second attachmentpoints of the plurality of conductive traces in multiple rows extendingadjacent the perimeter portion of the surface of the transparentsubstrate.
 4. The method according to claim 1, wherein forming aplurality of conductive traces on a surface of a transparent substratecomprises: disposing a conductive or conductor filled material onto thesecond surface of the transparent substrate in a pattern defining theplurality of conductive traces.
 5. The method according to claim 1,wherein forming a plurality of conductive traces on a surface of atransparent substrate comprises: disposing a layer of conductivematerial on the surface of the transparent substrate; and selectivelyetching the conductive material to define the plurality of conductivetraces.
 6. The method according to claim 1, further comprising:depositing a bead of sealant material on the second surface of thetransparent substrate along at least one side of the opticallyinteractive electronic device and in contact therewith.
 7. The methodaccording to claim 6, wherein the sealant material is selected tocomprise one of epoxy and silicone.
 8. The method according to claim 1,wherein the at least one discrete conductive element is selected tocomprise one of a solder ball, a solder column, a conductive epoxy, anda conductor-filled epoxy.
 9. The method according to claim 1, whereinthe optically interactive electronic device is selected to comprise animage sensor.
 10. The method according to claim 1, further comprising:mounting a plurality of optically interactive electronic devices on asingle transparent substrate; and dividing the transparent substrate toprovide individual electronic device packages.
 11. A method forfabricating an electronic device package comprising: providing asecondary substrate having a central aperture and a plurality ofconductive traces formed around the central aperture, each conductivetrace of the plurality of conductive traces having a first attachmentpoint and a second attachment point on a second surface of the secondarysubstrate; securing a first surface of the secondary substrate to asurface of a transparent substrate with the transparent substrateextending over the central aperture; providing an optically interactiveelectronic device having at least one bond pad on an active surfacethereof; bonding the at least one bond pad of the optically interactiveelectronic device to the first attachment point of a conductive trace ofthe plurality of conductive traces; and attaching at least one discreteconductive element to the second attachment point of the conductivetrace such that the at least one discrete conductive element extendsoutwardly from the secondary substrate within an outside perimeterthereof from the second attachment point in a direction perpendicular toa plane of the second surface of the secondary substrate and to a levelbeyond a back surface of the optically interactive electronic device.12. The method according to claim 11, further comprising: forming thesecond attachment points of the plurality of conductive traces in atleast one row extending adjacent a perimeter portion of the secondsurface of the secondary substrate.
 13. The method according to claim12, further comprising: forming the second attachment points of theplurality of conductive traces in multiple rows extending adjacent theperimeter portion of the second surface of the secondary substrate. 14.The method according to claim 11, wherein the secondary substrate isselected to comprise one of a printed circuit board, a polyimide film aceramic and silicon.
 15. The method according to claim 11, wherein theoutside perimeter of the secondary substrate is configured to besubstantially equal to an outside perimeter of the transparentsubstrate.
 16. The method according to claim 11, further comprising:depositing a bead of sealant material on the second surface of thesecondary substrate along at least one side of the optically interactiveelectronic device and in contact therewith.
 17. The method according toclaim 16, wherein the sealant material is selected to comprise one ofepoxy and silicone.
 18. The method according to claim 11, wherein the atleast one discrete conductive element is selected to comprise one of asolder ball, a solder column, a conductive epoxy, and a conductor-filledepoxy.
 19. The method according to claim 11, wherein the opticallyinteractive electronic device is selected to comprise an image sensor.20. The method according to claim 11, further comprising: mounting aplurality of optically interactive electronic device packages on asingle transparent substrate; and dividing the transparent substrate toprovide individual electronic device packages.
 21. A method forassembling an electronic device package comprising: forming a pluralityof conductive traces on a surface of a transparent substrate, eachconductive trace of the plurality of conductive traces having a firstattachment point and a second attachment point; providing an opticallyinteractive electronic device having at least one bond pad on an activesurface thereof; bonding the at least one bond pad of the opticallyinteractive electronic device to the first attachment point of aconductive trace of the plurality of conductive traces; providing abacking cap having at least one attachment pad on a surface of thebacking cap; and attaching the backing cap to the transparent substrateto cover a back surface of the optically interactive electronic deviceand provide electrical communication between the second attachment pointof the conductive trace and the at least one attachment pad on thesurface of the backing cap.
 22. The method according to claim 21,wherein attaching the backing cap to the transparent substrate comprisesforming a bond between the at least one backing cap attachment point andthe second attachment point of the conductive trace, the bond beingselected to comprise one of a conductive or conductor filled epoxy, asolder joint and a layer of anisotropically conductive adhesivematerial.
 23. The method according to claim 21, further comprising:forming an array of attachment pads on the surface of the backing cap.24. The method according to claim 21, further comprising: providing adiscrete conductive element on the at least one attachment pad on thesurface of the backing cap.
 25. The method according to claim 24,wherein the discrete conductive element is selected to comprise one of asolder ball, a solder column, a conductive epoxy, and a conductor-filledepoxy.
 26. The method according to claim 21, wherein forming a pluralityof conductive traces on a surface of a transparent substrate comprises:disposing a conductive or conductor filled material onto the surface ofthe transparent substrate in a pattern to define the plurality ofconductive traces.
 27. The method according to claim 21, wherein forminga plurality of conductive traces on a surface of a transparent substratecomprises: disposing a layer of conductive material on the surface ofthe transparent substrate; and selectively etching the conductivematerial.
 28. The method according to claim 21, wherein the opticallyinteractive electronic device is selected to comprise an image sensor.29. The method according to claim 21, further comprising: mounting aplurality of optically interactive electronic devices to a singletransparent substrate; and dividing the transparent substrate to provideindividual electronic device packages.
 30. A method for assembling anelectronic device package comprising: providing a secondary substratehaving a central aperture and a plurality of conductive traces formedaround the central aperture, each conductive trace of the plurality ofconductive traces having a first attachment point and a secondattachment point on a second surface of the secondary substrate;securing a first surface of the secondary substrate to a surface of atransparent substrate with the transparent substrate extending over thecentral aperture; providing an optically interactive electronic devicehaving at least one bond pad on an active surface thereof; bonding theat least one bond pad of the optically interactive electronic device tothe first attachment point of a conductive trace of the plurality ofconductive traces; providing a backing cap having at least oneattachment pad on a second surface of the backing cap; and attaching thebacking cap to the secondary substrate to cover a back surface of theoptically interactive electronic device and provide electricalcommunication between the second attachment point of the conductivetrace and the at least one attachment pad on the surface of the backingcap.
 31. The method according to claim 30, wherein attaching the backingcap to the secondary substrate comprises forming a bond between the atleast one backing cap attachment point and the second attachment pointof the conductive trace, the bond being selected to comprise one of aconductive or conductor-filled epoxy, a solder joint and a layer ofanisotropically conductive adhesive material.
 32. The method accordingto claim 30, further comprising: forming an array of attachment pads onthe surface of the backing cap.
 33. The method according to claim 30,further comprising: disposing a discrete conductive element on the atleast one attachment pad on the second surface of the backing cap. 34.The method according to claim 33, wherein the discrete conductiveelement is selected to comprise one of a solder ball, a solder column, aconductive epoxy, and a conductor-filled epoxy.
 35. The method accordingto claim 30, wherein the secondary substrate is selected to comprise oneof a printed circuit board, a polyimide film, a ceramic and silicon. 36.The method according to claim 30, wherein an outside perimeter of thesecondary substrate is formed to be substantially equal to an outsideperimeter of the transparent substrate.
 37. The method according toclaim 30, wherein the optically interactive electronic device isselected to comprise an image sensor.
 38. The method according to claim30, further comprising: assembling a plurality of optically interactiveelectronic device packages on a single transparent substrate; anddividing the transparent substrate to provide individual electronicdevice packages.
 39. A method for assembling an electronic devicepackage comprising: providing a flexible substrate having a mountingportion with a central aperture and a backing portion; forming aplurality of conductive traces on the flexible substrate, eachconductive trace of the plurality of conductive traces having a firstattachment point on a first side of the flexible substrate formedsubstantially adjacent the central aperture of the mounting portion, anda second attachment point formed on the backing portion on a second sideof the flexible substrate; securing a second side of the flexiblesubstrate to a surface of a transparent substrate with the transparentsubstrate extending over the central aperture; providing an opticallyinteractive electronic device having at least one bond pad on an activesurface thereof; bonding the at least one bond pad of the opticallyinteractive electronic device to the first attachment point of aconductive trace of the plurality of conductive traces; and bending overthe backing portion of the flexible substrate such that the backingportion is positioned substantially adjacent a back surface of theoptically interactive electronic device.
 40. The method according toclaim 39, further comprising: depositing a bead of sealant material onthe first side of the flexible substrate along at least one side of theoptically interactive electronic device. 41 The method according toclaim 40, wherein the sealant material is selected to comprise one ofepoxy and silicone.
 42. The method according to claim 39, furthercomprising: securing a second side of a rigid substrate to the backingportion on the first side of the flexible substrate.
 43. The methodaccording to claim 39, further comprising: adhesively attaching thebacking portion to the back surface of the optically interactiveelectronic device.
 44. The method according to claim 42, furthercomprising: forming at least one stand-off structure on the first sideof the rigid substrate; and attaching the at least one stand-offstructure to the mounting portion on the first side of the flexiblesubstrate.
 45. The method according to claim 39, further comprising:forming the second attachment points of the plurality of conductivetraces in an array pattern on the backing portion on the second side ofthe flexible substrate.
 46. The method according to claim 39, furthercomprising: attaching a discrete conductive element to the secondattachment point of the conductive trace.
 47. The method according toclaim 46, wherein the discrete conductive element is selected tocomprise one of a solder ball, a solder column, a conductive epoxy, anda conductor-filled epoxy.
 48. The method according to claim 39, whereinthe optically interactive electronic device is selected to comprise animage sensor.
 49. The method according to claim 39, further comprising:mounting a plurality of optically interactive electronic devices to asingle transparent substrate; and dividing the transparent substrate toprovide individual electronic device packages.